Management of working fluid during heat engine system shutdown

ABSTRACT

Provided herein are a heat engine system and a method for managing a working fluid in the heat engine system during an emergency shutdown. The heat engine system utilizes a working fluid (e.g., sc-CO2) contained within a working fluid circuit to absorb and transport heat. An inventory system is coupled to the working fluid circuit and configured to receive and store at least a portion of the working fluid in the working fluid circuit during an emergency shutdown process. An attemperation line is coupled to the working fluid circuit upstream one or more heat exchangers and configured to direct a portion of the working fluid flow around at least one or more heat exchangers, thereby managing the temperature of the working fluid in the working fluid circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Prov. Appl. No. 61/777,014, filed on Mar. 12, 2013, the contents of which are hereby incorporated by reference to the extent not inconsistent with the present disclosure.

BACKGROUND

Waste heat is often created as a byproduct of industrial processes where a heat source stream of high-temperature liquids, gases, or fluids must be exhausted into the environment or removed in some way in an effort to maintain the operating temperatures of the industrial process equipment. Some industrial processes utilize heat exchange devices to capture and recycle waste heat through other process streams. However, the capturing and recycling of waste heat is generally infeasible by industrial processes that utilize high temperatures or have insufficient mass flow or other unfavorable conditions.

The waste heat from the heat source stream can be converted into useful energy by a variety of turbine generator or heat engine systems that employ thermodynamic methods, such as Rankine cycles. Rankine cycles and similar thermodynamic methods are typically steam-based processes that recover and utilize waste heat to generate steam from water to drive a turbine, turbo, or other expander. An organic Rankine cycle utilizes a lower boiling-point working fluid, instead of water, during a traditional Rankine cycle. Exemplary lower boiling-point working fluids include hydrocarbons, such as light hydrocarbons (e.g., propane or butane) and halogenated hydrocarbons, such as hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) (e.g., R245fa). More recently, in view of issues such as thermal instability, toxicity, flammability, and production cost of the lower boiling-point working fluids, some thermodynamic cycles have been modified to circulate non-hydrocarbon working fluids, such as ammonia.

The heat source stream may be a waste heat stream such as, but not limited to, a gas turbine exhaust stream, an industrial process exhaust stream, or other combustion product exhaust streams, such as furnace or boiler exhaust streams. In many cases, the temperature of the heat source stream may be as high as 1,000° C., or greater than 1,000° C. To capture and recycle the waste heat from these heat source streams with a heat engine system, a working fluid, circulating through a working fluid circuit, is flowed through the heat exchangers of a waste heat system to absorb the thermal energy therein and transfer the absorbed thermal energy to a turbine power generator to produce electricity.

During an emergency shutdown, or a system shutdown, the circulation of the working fluid may be stopped, resulting in a trapped volume of the working fluid within the waste heat system. Further, during a system shutdown, the heat source stream in the waste heat system may continue to flow, thereby increasing the temperature and pressure of the working fluid entrained therein over their intended design limits. To avoid excessive pressures, the heated working fluid is often vented to the atmosphere resulting in a loss of working fluid that must be subsequently replenished. The process of replenishing the vented working fluid contributes to an overall loss of efficiency and increased costs as the process requires expending time and energy. An alternative method to avoid excessive working fluid pressure is to vent the working fluid through the working fluid circuit to another part of the heat engine system. Such a method may involve flowing the high pressure working fluid to an integrated sub-system of the heat engine system. However, the high temperature of the working fluid may damage one or more components of the heat engine system not designed for such high temperatures.

Therefore, there is a need for a heat engine system and a method for managing a volume of a working fluid during a system shutdown, wherein the temperature and pressure may be regulated to avoid the venting of the working fluid, and avoid damage to components of the heat engine system.

SUMMARY

Embodiments of the disclosure provide a heat engine system including a working fluid containing a working fluid in a working fluid circuit. The working fluid circuit may have a high pressure side and a low pressure side, wherein a portion of the working fluid is in a supercritical state in the high pressure side of the working fluid circuit. The heat engine system may further include at least one heat exchanger in the working fluid circuit in thermal communication with a heat source stream coupled to the working fluid circuit, wherein the heat exchanger is configured to provide thermal energy from the heat source stream to the working fluid in the working fluid circuit. A power turbine may be disposed between the high pressure side and the low pressure side of the working fluid circuit and may be configured to convert a pressure drop in the working fluid to mechanical energy. The system may further include a recuperator in the working fluid circuit, configured to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit. A turbo pump may be coupled to the low pressure side and the high pressure side of the working fluid circuit and may be operative to flow the working fluid through the working fluid circuit.

In another embodiment, the system may include an attemperation line and an attemperation valve disposed within the working fluid circuit. The attemperation line may be coupled to the working fluid circuit upstream of at least one or more heat exchangers and downstream of at least one heat exchanger and may be configured to circumvent the working fluid around at least one or more heat exchangers. The system may further include a power turbine bypass line and a power turbine bypass valve disposed in the working fluid circuit. The power turbine bypass line may be fluidly coupled to the working fluid circuit upstream of the power turbine and downstream of the power turbine, and may be configured to circumvent the working fluid around the power turbine. The system may further include an inventory system coupled to the working fluid circuit configured to receive at least a portion of the working fluid from the working fluid circuit during an emergency shutdown process.

In one or more embodiments described herein, a method for managing a working fluid in a heat engine system during an emergency shutdown process includes circulating the working fluid in a working fluid circuit having a high pressure side and a low pressure side, wherein at least a portion of the working fluid is in a supercritical state. The method further includes preventing the venting of the working fluid through one or more pressure relief valves by flowing the working fluid through a power turbine bypass line, thereby circumventing the working fluid around a power turbine. The method further includes cooling the working fluid in the heat engine system by flowing a portion of the working fluid through an attemperation line and combining the portion of the working fluid in the attemperation line with a second portion of working fluid downstream of one or more heat exchangers.

The method further includes discharging the working fluid in the working fluid circuit to an inventory tank, regulating the temperature of the inventory tank, and regulating the pressure of the inventory tank. In at least one embodiment, the method of regulating the temperature or the pressure may include providing two refrigeration systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure are best understood from the following detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates an exemplary heat engine system, according to one or more embodiments disclosed herein.

FIG. 2 illustrates an exemplary heat engine system, according to one or more embodiments disclosed herein.

FIG. 3 is a flow chart illustrating a method for managing the working fluid in a heat engine system during a system shutdown, according to one or more embodiments disclosed herein.

DETAILED DESCRIPTION

It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure, however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure.

Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Further, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. Furthermore, as it is used in the claims or specification, the term “or” is intended to encompass both exclusive and inclusive cases, i.e., “A or B” is intended to be synonymous with “at least one of A and B,” unless otherwise expressly specified herein.

FIG. 1 depicts an exemplary heat engine system 90 containing an inventory system 180 fluidly coupled to a working fluid circuit 102 of the heat engine system 90. The heat engine system 90 may also be referred to as a thermal engine, a power generation device, a heat or waste heat recovery system, and a heat to electricity system, or derivatives thereof. The heat engine system 90 further contains a waste heat system 100 and a power generation system 127 coupled to and in thermal communication with each other through a working fluid circuit 102. The heat engine system 90 may be configured to encompass one or more elements of a Rankine cycle, a derivative of a Rankine cycle, or another thermodynamic cycle for generating electrical energy from a wide range of thermal sources.

As depicted in FIG. 1, the working fluid circuit 102 may contain a high pressure side, represented as, “—”, and a low pressure side, represented as “—••—••”. The working fluid circuit 102 may further contain a working fluid (e.g., sc-CO₂), wherein the working fluid may circulate within the high and low pressure sides of the working fluid circuit 102. The use of the term “working fluid” may be not intended to limit the state or phase of matter of the working fluid. For instance, the working fluid or portions of the working fluid may be in a liquid phase, a gas phase, a fluid phase, a supercritical state, a subcritical state, or any other phase or state at any one or more points within the heat engine system 90 or thermodynamic cycle. In one or more embodiments, the working fluid may be in a supercritical state over certain portions of the working fluid circuit 102 of the heat engine system 90 (e.g., a high pressure side) and in a subcritical state over other portions of the working fluid circuit 102 of the heat engine system 90 (e.g., a low pressure side). In other embodiments, the entire thermodynamic cycle may be operated such that the working fluid may be maintained in either a supercritical or subcritical state throughout the entire working fluid circuit 102 of the heat engine system 90.

Generally, in some embodiments, the high pressure side of the working fluid circuit 102 contains the working fluid (e.g., sc-CO₂) at a pressure of about 15 MPa or greater, such as about 17 MPa or greater or about 20 MPa or greater. In some examples, the high pressure side of the working fluid circuit 102 may have a pressure within a range from about 15 MPa to about 30 MPa, more narrowly within a range from about 16 MPa to about 26 MPa, more narrowly within a range from about 17 MPa to about 25 MPa, and more narrowly within a range from about 17 MPa to about 24 MPa, such as about 23.3 MPa. In other examples, the high pressure side of the working fluid circuit 102 may have a pressure within a range from about 20 MPa to about 30 MPa, more narrowly within a range from about 21 MPa to about 25 MPa, and more narrowly within a range from about 22 MPa to about 24 MPa, such as about 23 MPa.

The low pressure side of the working fluid circuit 102 may contain the working fluid (e.g., CO₂ or sub-COO at a pressure of less than 15 MPa, such as about 12 MPa or less or about 10 MPa or less. In some examples, the low pressure side of the working fluid circuit 102 may have a pressure within a range from about 4 MPa to about 14 MPa, more narrowly within a range from about 6 MPa to about 13 MPa, more narrowly within a range from about 8 MPa to about 12 MPa, and more narrowly within a range from about 10 MPa to about 11 MPa, such as about 10.3 MPa. In other examples, the low pressure side of the working fluid circuit 102 may have a pressure within a range from about 2 MPa to about 10 MPa, more narrowly within a range from about 4 MPa to about 8 MPa, and more narrowly within a range from about 5 MPa to about 7 MPa, such as about 6 MPa.

In some examples, the high pressure side of the working fluid circuit 102 may have a pressure within a range from about 17 MPa to about 23.5 MPa, and more narrowly within a range from about 23 MPa to about 23.3 MPa while the low pressure side of the working fluid circuit 102 may have a pressure within a range from about 8 MPa to about 11 MPa, and more narrowly within a range from about 10.3 MPa to about 11 MPa.

An attemperation line 160 may fluidly couple a fluid line 131 of the working fluid circuit 102 upstream of one or more heat exchangers 120, 130. The attemperation line 160 may further fluidly couple a fluid line 139 of the working fluid circuit 102 downstream of one or more heat exchangers 120, 130. An attemperation valve 162 may be disposed within the attemperation line and may be configured to control the flow therethrough. The attemperation valve 162 may be adjusted to one or more positions to control the flow of the working fluid within the working fluid circuit 102 during one or more modes of operation for the heat engine system 90 described herein. In at least one position, the attemperation valve 162 may allow the working fluid upstream of one or more heat exchangers 120, 130 to flow through the attemperation valve 162, through the attemperation line 160, and the fluid lines therebetween, thereby avoiding at least one or more heat exchangers 120, 130. In a second position, the attemperation valve 162 may be configured to flow the working fluid upstream of one or more heat exchangers 120, 130 through one or more heat exchangers 120, 130, and the fluid lines therebetween. In one embodiment, the temperature of working fluid flowing through one or more heat exchangers 120, 130 may be greater than the temperature of the working fluid flowing through the attemperation line 160.

A power turbine bypass line 119 may fluidly couple the fluid line 139 upstream of the power generation system 127 to a fluid line 138 downstream of the power generation system 127. A power turbine bypass valve 118 may be disposed within the power turbine bypass line 119 and may be configured to control the flow of working fluid therethrough. The power turbine bypass valve 118 may be adjusted to one or more positions to control the flow of the working fluid within the working fluid circuit 102 during one or more modes of operation for the heat engine system 90 described herein. In at least one position, the power turbine bypass valve 118 may allow at least a portion of the working fluid upstream of the power generation system 127 to flow through the power turbine bypass valve 118, through the power turbine bypass line 119, and through the fluid lines therebetween, thereby avoiding the power generation system 127. In a second position, the power turbine bypass valve 118 may allow the working fluid upstream of the power generation system 127 to flow through the power generation system 127, and through the fluid lines therebetween. In one or more embodiments, the power turbine bypass valve 118 may be modulated or controlled to regulate the flow to and through the power generation system 127.

A power turbine stop valve 117 may be disposed within the working fluid circuit 102 upstream of the power generation system 127 and may be configured to control the flow of the working fluid therethrough. The power turbine stop valve 117 may be adjusted to one or more positions to control the flow of the working fluid within the working fluid circuit 102 during one or more modes of operation for the heat engine system 90 described herein. In one or more embodiment, the power turbine stop valve 117 may be actuated or configured to stop or substantially prevent the flow of working fluid to and through the power generation system 127.

The heat engine system 90 may also contain one or more recuperators 116 fluidly coupled in series to the low pressure side of the working fluid circuit 102. The one or more recuperators 116 may be operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit 102. In one or more embodiments, a first recuperator 116 may be fluidly coupled to the low pressure side of the working fluid circuit 102, disposed downstream of the working fluid outlet of the power turbine 128, and upstream of a second recuperator (not shown) and/or a condenser 174, and may be configured to remove at least a portion of thermal energy from the working fluid discharged from the power turbine 128. The first recuperator 116 may also be fluidly coupled to the high pressure side of the working fluid circuit 102, disposed upstream of the first heat exchanger 120 and/or the working fluid inlet of the power turbine 128, and downstream of the second heat exchanger 130, and configured to increase the amount of thermal energy in the working fluid prior to flowing into the first heat exchanger 120 and/or the power turbine 128. Therefore, the first recuperator 116 may be configured to cool the low pressurized working fluid discharged downstream of the power turbine 128 and/or configured to heat the high pressurized working fluid entering into or upstream of the first heat exchanger 120 and/or the power turbine 128.

The heat engine system 90 may also contain one or more condensers 174 fluidly coupled to the low pressure side of the working fluid circuit 102 upstream of one or more pumps 179. The condenser 174 may be fluidly coupled to a cooling system (not shown) that receives a cooling fluid from a cooling fluid supply and returns the warmed cooling fluid to the cooling system through a cooling fluid return. The cooling fluid may be water, carbon dioxide, any other aqueous, inorganic and/or organic fluid, and/or any other mixtures thereof that may be maintained at a lower temperature than the working fluid. In one embodiment, an additional condenser or cooler (not shown) may be fluidly coupled to one or more recuperators 116 and in thermal communication with the low pressure side of the working fluid circuit 102. The additional condenser or cooler may be operative to control the temperature of the working fluid in the low pressure side of the working fluid circuit 102.

The heat engine system 90 may further include a pump 179 disposed between the high and low pressure sides of the working fluid circuit 102 to circulate the working fluid therethrough. The pump 179 may be a turbo-drive pump, a motor drive pump (e.g., mechanical or electric motor), or a pumping system having two or more pumps. In some examples, the pump 179 may be a pumping system containing a motor-drive pump and a turbo-drive pump, wherein the motor-drive pump may be used to start the circulation of the working fluid and the turbo-drive pump may be used to maintain the circulation of the working fluid throughout the electrical energy generating process.

The heat engine 90 may further include one or more throttle valves 150 disposed within the working fluid circuit 102 downstream of the pump 179. The throttle valve 150 may be actuated or modulated to regulate the circulation of the working fluid throughout the working fluid circuit 102. In one or more embodiments, the throttle valve 150 may be configured to control the flow of the working fluid throughout the working fluid circuit 102. The throttle valve may also substantially control the flow of the working fluid from the pump 179 through the working fluid circuit 102. In at least one embodiment, a second throttle valve (not shown) may be disposed within the high pressure side of the working fluid circuit 102, upstream of one or more heat exchangers 120, 130 and downstream of the pump 179. The second throttle valve may be a throttle trim valve configured to control the flow of the working fluid through the working fluid circuit 102. In at least one embodiment, the throttle trim valve and the throttle valve 150 may both control the flow of the working fluid in the working fluid circuit 102.

In at least one embodiment, the working fluid circuit 102 may provide one or more relief valves 113 a and 113 b and one or more corresponding relief outlets 114 a and 114 b, wherein the relief valves 113 a and 113 b and the relief outlets 114 a and 114 b are in fluid communication with each other, respectively. Under nominal operating conditions, such as during an electricity generation process, the release valves 113 a and 113 b may remain closed. The relief valves 113 a and 113 b may also be configured to automatically open to relieve an excess pressure at a predetermined valve within the working fluid, whereupon the excess working fluid may flow through the relief valves 113 a and 113 b to the corresponding relief outlets 114 a and 114 b. In at least one embodiment, the relief outlets 114 a and 114 b may provide a path for the excess working fluid to flow into the ambient surroundings, thereby venting the excess working fluid to the atmosphere. The relief outlets 114 a and 114 b may also provide a path for the excess working fluid to flow into a recycling or reclamation step that may include capturing, condensing, and/or storing the working fluid. As shown in FIG. 1, the heat engine system 90 includes a first relief valve 113 a and a first relief outlet 114 a disposed in and fluidly coupled to the working fluid circuit 102 downstream of the first heat exchanger 120 and upstream of the power turbine 128. A second relief valve 113 b and a second relief outlet 114 b may be disposed in and fluidly coupled to a fluid line of the working fluid circuit 102 between the waste heat system 100 and the pump 179.

As shown in FIG. 1, the waste heat system 100 may include a heat source stream 110 and one or more heat exchangers 120, 130, wherein the heat source stream 110 may flow through one or more heat exchangers 120, 130 disposed within the waste heat system 100. The waste heat system 100 of the heat engine system 90 contains two heat exchangers 120, 130 fluidly coupled to the high pressure side of the working fluid circuit 102 and in thermal communication with the heat source stream 110. Thermal communication provides the transfer of thermal energy from the heat source stream 110 to the working fluid flowing therethrough. Each of the heat exchangers 120, 130 may be fluidly coupled to and in thermal communication with the heat source stream 110 and independently coupled to and in thermal communication with the working fluid within the working fluid circuit 102. In one or more embodiments disclosed herein, the one or more heat exchangers 120, 130 fluidly coupled to the working fluid circuit 102 may include a primary heat exchanger, a secondary heat exchanger, and/or a tertiary heat exchanger. A first heat exchanger 120 may be the primary heat exchanger fluidly coupled to the working fluid circuit 102 upstream of an inlet of a power turbine 128. A second heat exchanger 130 may be fluidly coupled to the working fluid circuit 102 upstream of an inlet of the first heat exchanger 120. A third heat exchanger (not shown) may be fluidly coupled to the working fluid circuit 102 upstream of the inlet of the first heat exchanger 120 and/or downstream of the second heat exchanger 130.

The waste heat system 100 may include an inlet 104 for receiving the heat source stream 110 and an outlet 106 for discharging the heat source stream 110 out of the waste heat system 100. The heat source stream 110 may be introduced to the inlet 104, flow through the inlet 104, through the first heat exchanger 120, through the second heat exchanger 130, and/or through any additional heat exchangers fluidly coupled to the heat source stream 110, and through the outlet 106. The heat source stream 110 may also be routed to flow through the first and second heat exchangers 120, 130 and/or any additional heat exchangers in other desired sequences.

The heat source stream 110 may be a waste heat stream such as, but not limited to, a gas turbine exhaust stream, an industrial process exhaust stream, or any other combustion product exhaust stream, such as a furnace or boiler exhaust stream. The heat source stream 110 may be at a temperature within a range from about 100° C. to about 1,000° C., or greater than 1,000° C., and in some examples, within a range from about 200° C. to about 800° C., more narrowly within a range from about 300° C. to about 600° C. The heat source stream 110 may contain air, carbon dioxide, carbon monoxide, water or steam, nitrogen, oxygen, argon, derivatives thereof, or mixtures thereof. In some embodiments, the heat source stream 110 may derive thermal energy from renewable sources of thermal energy, such as solar or geothermal sources.

In some embodiments, the types of working fluid that may be circulated, flowed, or otherwise utilized in the working fluid circuit 102 include carbon oxides, hydrocarbons, alcohols, ketones, halogenated hydrocarbons, ammonia, amines, aqueous, or combinations thereof. Exemplary working fluids that may be utilized in the working fluid circuit 102 include carbon dioxide, ammonia, methane, ethane, propane, butane, ethylene, propylene, butylene, acetylene, methanol, ethanol, acetone, methyl ethyl ketone, water, derivatives thereof, or mixtures thereof. Halogenated hydrocarbons may include hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) (e.g., 1,1,1,3,3-pentafluoropropane (R245fa)), fluorocarbons, derivatives thereof, or mixtures thereof.

In many embodiments described herein, the working fluid circulated, flowed, or otherwise utilized in the working fluid circuit 102, and the other exemplary circuits disclosed herein, may contain carbon dioxide (CO₂) and mixtures containing carbon dioxide. Generally, at least a portion of the working fluid circuit 102 contains the working fluid in a supercritical state (e.g., sc-CO₂). Carbon dioxide utilized as the working fluid or contained in the working fluid for power generation cycles has many advantages over other compounds typically used as working fluids, since carbon dioxide has the properties of being non-toxic and non-flammable and is also easily available and relatively inexpensive. Due in part to a relatively high working pressure of carbon dioxide, a carbon dioxide system may be much more compact than systems using other working fluids. The high density and volumetric heat capacity of carbon dioxide with respect to other working fluids makes carbon dioxide more “energy dense” meaning that the size of all system components can be considerably reduced without losing performance. It should be noted that use of the terms carbon dioxide (CO₂), supercritical carbon dioxide (sc-CO₂), or subcritical carbon dioxide (sub-CO₂) is not intended to limit carbon dioxide of any particular type, source, purity, or grade. For example, industrial grade carbon dioxide may be contained in and/or used as the working fluid without departing from the scope of the disclosure.

In other exemplary embodiments, the working fluid in the working fluid circuit 102 may be a binary, ternary, or other working fluid blend. The working fluid blend or combination can be selected for the unique attributes possessed by the fluid combination within a heat recovery system, as described herein. For example, one such fluid combination includes a liquid absorbent and carbon dioxide mixture enabling the combined fluid to be pumped in a liquid state to high pressure with less energy input than required to compress carbon dioxide. In another exemplary embodiment, the working fluid may be a combination of carbon dioxide (e.g., sub-CO₂ or sc-CO₂) and one or more other miscible fluids or chemical compounds. In yet other exemplary embodiments, the working fluid may be a combination of carbon dioxide and propane, or carbon dioxide and ammonia, without departing from the scope of the disclosure.

The power generation system 127 may include a power turbine 128 and a power generator 129. The power turbine 128 may be disposed between the high pressure side and the low pressure side of the working fluid circuit 102, downstream of the first heat exchanger 120, and fluidly coupled to and in thermal communication with the working fluid circuit 102, and operationally coupled to the power generator 129. The power turbine 128 may be configured to convert a pressure drop in the working fluid to mechanical energy whereby the absorbed thermal energy of the working fluid may be transformed to mechanical energy of the power turbine 128. Therefore, the power turbine 128 may be an expansion device capable of transforming a pressurized fluid into mechanical energy, generally, transforming high temperature and pressure fluid into mechanical energy, such as rotating a shaft.

The power turbine 128 may contain or be a turbine, a turbo, an expander, or another device for receiving and expanding the working fluid discharged from the first heat exchanger 120. The power turbine 128 may have an axial construction or radial construction and may be a single-staged device or a multi-staged device. Exemplary turbines that may be utilized in power turbine 128 include an expansion device, a geroler, a gerotor, a valve, other types of positive displacement devices such as a pressure swing, a turbine, a turbo, or any other device capable of transforming a pressure or pressure/enthalpy drop in a working fluid into mechanical energy. A variety of expanding devices are capable of working within the inventive system and achieving different performance properties that may be utilized as the power turbine 128. The power generator 129 may be a generator, an alternator (e.g., permanent magnet alternator), or other device for generating electrical energy, such as transforming mechanical energy from a shaft and the power turbine 128 to electrical energy.

In one or more embodiments, the overall efficiency of the heat engine system 90, wherein at least a portion of the working fluid contains supercritical carbon dioxide, may be influenced by the inlet or suction pressure at one or more pumps 179. In order to minimize and/or regulate the suction pressure of the pump, the heat engine system 90 may incorporate the use of a mass management system (“MMS”) 170. The mass management system may be fluidly coupled to the high pressure side and/or the low pressure side of the heat engine system 90. In at least one embodiment, the mass management system 170 may control the inlet pressure of one or more pumps 179 by regulating the amount of working fluid entering and/or exiting the heat engine system 90 at one or more strategic locations in the working fluid circuit 102, such as at one or more connection points, inlets/outlets, valves, and/or conduits throughout the heat engine system 90. Thus, the mass management system 170 may influence the overall efficiency of the heat engine system 90 by regulating the pressure ratio at the pumps 179. In at least one embodiment, the efficiency of the heat engine system 90 may be increased by maximizing the pressure ratio for the pumps 179.

In one or more embodiments, the mass management system 170 may operate semi-passively with the heat engine system 90. The heat engine system 90 may include sensors disposed throughout the working fluid circuit 102 to monitor pressures, temperatures, and/or flowrates of the working fluid therein. The mass management system 170 may also include one or more valves, mass management tanks, tank heaters, or other components that may facilitate the movement of the working fluid to and from the heat engine system 90. In one or more embodiment, a mass management tank (not shown) of the mass management system 170 may include a coil disposed within the mass management tank to add or remove heat, thereby controlling the pressure and/or the temperature in the mass management tank. By controlling the pressure and/or the temperature within the mass management tank, the movement or flow of the working fluid in and out of the heat engine system 90 may be regulated. Alternatively, mechanical means, such as a pump, may be used to move or flow the working fluid from the mass management tank into the heat engine system 90.

Exemplary embodiments of the mass management system 170 and a range of variations thereof, are disclosed in U.S. application Ser. No. 13/278,705, filed Oct. 21, 2011, published as U.S. Pub. No. 2012-0047892, and issued as U.S. Pat. No. 8,613,195, the contents of which are incorporated herein by reference to the extent consistent with the present disclosure.

The heat engine system may also include a fluid fill system 140 operatively coupled to the working fluid circuit 102 and/or one or more external sources or systems, and configured to deliver supplemental working fluid to the working fluid circuit 102 and/or one or more external sources or systems, such as the mass management system 170. The fluid fill system 140 may also be configured to receive supplemental working fluid from the working fluid circuit 102 and/or one or more external sources or systems, such as the mass management system 170. The fluid fill system 140 may be fluidly coupled to the heat engine system 90 in one or more ways. In at least one embodiment, the fluid fill system 140 may contain a fluid supply tank, wherein the fluid supply tank may be fluidly coupled to the working fluid circuit 102 through one or more lines and/or valves. In another embodiment, the fluid supply tank (not shown) may be fluidly coupled to the mass management tank (not shown) of the mass management system 170. Thus, the mass management tank may be configured to collect and recycle working fluid collected in the fluid fill system 140 back into the heat engine system 90, thereby providing the heat engine system 90 with a constant supply of additional and/or supplemental working fluid. An exemplary fluid supply tank may include, but is not limited to, a Dewar-type vessel, or any other vessel capable of storing the working fluid in the heat engine system 90. In one or more embodiments, a pressure differential may drive the flow of the working fluid between the fluid fill system 140 and one or more systems in the heat engine system 90. For example, a high pressure differential between the fluid fill system 140 and the low-pressure side of the working fluid circuit 102 may drive the working fluid from the fluid fill system 140 to the working fluid circuit 102 without the aid of a pump.

Exemplary fluid fill systems are described and illustrated in U.S. application Ser. No. 12/880,428, filed Sep. 13, 2010, and issued as U.S. Pat. No. 8,281,593, the contents of which are incorporated herein by reference to the extent consistent with the present disclosure.

The heat engine system 90 may further include an inventory system 180 operatively coupled to the working fluid circuit 102 and configured to receive and/or store a volume of the working fluid discharged from the heat engine system 90. In at least one embodiment, the inventory system 180 may be coupled to the low pressure side of the working fluid circuit 102, thereby utilizing the pressure differential of the low pressure side relative to the high pressure side of the working fluid circuit 102 to facilitate the flow of the working fluid. The inventory system 180 may also be fluidly coupled to one or more systems and configured to deliver or recycle the working fluid back to one or more systems of the heat engine system 90, including, but not limited to the mass management system 170, the fluid fill system 140, the working fluid circuit 102, the power generation system 127, and/or the heat engine system 102.

The inventory system 180 may be sized or configured to receive and store all or substantially all of the working fluid in the working fluid circuit 102 of the heat engine system 90. In at least one embodiment, the inventory system may be configured to receive and store all or substantially all the working fluid in the high pressure side of the working fluid circuit 102. In at least one embodiment, the amount of working fluid in the heat engine system 90 may depend, at least in part, upon the mode of operation or process that the heat engine system 90 is implementing. For example, the amount of working fluid in the heat engine system 90 when running in a full power mode may be about 3,000 kg more than when in an idle mode. In some cases, this excess working fluid may be within the high pressure side of the working fluid circuit and/or entrained within the waste heat system 100. The amount of working fluid in the heat engine system 90 may also depend upon the size of the system and/or design of the system.

The inventory system 180 may include one or more inventory tanks or vessels 181. As shown in FIG. 1, the inventory tank 181 may be fluidly coupled to the working fluid circuit 102 through an inventory system line 186, and an inventory flow valve 185 may be disposed therein to regulate the flow therethrough. In at least another embodiment, the inventory tank 181 may be coupled to the mass management system 170. An exemplary inventory tank may include a Dewar-type vessel, such as a liquid carbon dioxide holding container commercially available through gas and/or chemical suppliers, or any other vessel capable of storing the working fluid. In one or more embodiments, the inventory tank 181 may be rated for low-pressure applications. For example, the inventory tank 181 may have a maximum allowable working pressure (MAWP) rating of about 2.4 MPa (or about 350 pounds per square inch (psi)). A low-pressure rated inventory tank 181 may contribute to or provide a cost effective method to store the working fluid in the heat engine system 90.

The inventory tank 181 may be over-sized relative to the requirements for the working fluid in the working fluid circuit 102 of the heat engine system 90. For example, the inventory tank 181 may have a volume greater than the volume of the working fluid in the working fluid circuit 102. The inventory tank 181 may also be over-sized relative to the requirements for the working fluid in the working fluid circuit 102 and a heat engine working fluid leak. For example, the inventory tank 181 may provide enough volume for the liquid and vapor storage, while maintaining the internal pressure below the MAWP. The volume requirements of the inventory tank 181 may further include providing enough volume for the rapid discharge of a high temperature and/or pressure working fluid, while maintaining the pressure below the MAWP. For example, the size requirements of the inventory tank 181 during a normal shutdown procedure may be much less than during an emergency shutdown procedure. The size requirements of the inventory system during normal shutdown may be less than during an emergency shutdown procedure due to the differences in time required to discharge the working fluid for each process. For example, the normal shutdown process may last several hours. In at least one embodiment, the normal shutdown process may last from a low of about 1 hour, about 2 hours, about 3 hours, or more than 3 hours, to a high of about 4 hours, about 5 hours, about 6 hours, or more than 6 hours. In at least one embodiment, the normal shutdown process may include subjecting the working fluid to one or more methods of cooling or compression, thereby reducing the volume requirements of the inventory tank 181. The emergency shutdown process may last from a low of about less than 1 minute, about 1 minute, about 2 minutes, to a high of about 1 minute, about 2 minutes, or greater than 2 minutes, thus precluding the ability to either further compress or cool the working fluid before entering the inventory tank 181.

In at least one embodiment, the working fluid may be CO₂. Thus, as the working fluid is introduced into the inventory tank 181 at certain pressures and/or temperatures, the working fluid may transfer and/or absorb thermal energy or heat to/from the inventory tank 181. For example, if the inventory tank 181 is warmer relative to the working fluid, then the working fluid may absorb the thermal energy from the inventory tank 181 and begin evaporating. The absorption and evaporation event may continue until the surface of the tank cools to the saturation temperature for the given pressure. Conversely, if the inventory tank 181 is cooler relative to the working fluid, then the inventory tank 181 may absorb the thermal energy from the working fluid.

The inventory system 180 may also include one or more heat sinks (not shown) disposed therein or operationally coupled to the internal volume of the inventory tank 181. The heat sink may absorb at least a portion of the thermal energy from the working fluid in the inventory tank 181, thereby reducing and/or maintaining the pressure within the inventory tank 181 below the MAWP. The heat sink may include any apparatus or assembly capable of absorbing or dissipating thermal energy or heat from the working fluid, including but not limited to a cooler and/or a condenser. In at least one embodiment, the heat sink may be provided by an additional volume of a working fluid stored or maintained in the inventory tank 181 during nominal operating conditions. Thus, in at least one embodiment, the inventory tank 181 may be over-sized relative to the requirements for the working fluid in the heat engine system 90, the heat engine working fluid leak, and the additional volume of the working fluid serving as a heat sink. The inventory tank 181 may also include an insulating layer (not shown), wherein the insulating layer may reduce the transfer of thermal energy between the internal volume and an external source. In at least one embodiment, the external source may be the atmosphere.

The inventory system 180 may further include one or more refrigeration systems 182, 183 disposed therein and configured to maintain the temperature and/or pressure of the inventory tank 181. A first refrigeration system 182 may be coupled to the inventory tank 181 and sized to accommodate a normal shutdown process. In one embodiment, the first refrigeration system 182 may be configured to maintain the working fluid within the inventory tank 181 at a relatively low operating pressure and temperature. In another embodiment, the first refrigeration system 182 may be configured to restore the temperature and/or pressure back to normal operating conditions. For example, the first refrigeration system 182 may operate to maintain an internal pressure of the inventory tank 181 within a range from about 1.4 MPa to about 2.4 MPa and the working fluid contained therein may be continuously refrigerated or otherwise regulated in order to maintain a temperature within a range from about −31° C. to about −13° C. At least part of the working fluid contained in the inventory tank 181 may also be in a liquid state (e.g., liquid-CO₂).

A second refrigeration system 183 may be operationally coupled to the inventory tank 181 and configured to reduce and/or eliminate boil-off due to thermal absorption by the inventory tank 181 and/or through its insulating layer, thereby reducing and/or maintaining the pressure of the working fluid in the inventory tank 181 below the MAWP. In one or more embodiments, the second refrigeration system 183 may be smaller in size relative to the first refrigeration system 181 and may provide a cost effective method for managing the working fluid of the heat engine system 90. For example, the one or more refrigeration systems may provide a method to manage a high temperature and/or pressure working fluid without a high pressure rated inventory tank 181. In one embodiment, the refrigeration systems 182, 183 may maintain the internal pressure below the MAWP for a low-pressure rated Dewar during one or more modes of operating the heat engine system 90.

FIG. 2 depicts another exemplary heat engine system 200 containing a process system 210 and the power generation system 127 fluidly coupled to and in thermal communication with the waste heat system 100 through the working fluid circuit 102, as described in one of more embodiments herein. The pump 179 in FIG. 2 include two pumps, a turbo pump 260 and/or a start pump 280, disposed within the working fluid circuit 102 and fluidly coupled between the low pressure side and the high pressure side of the working fluid circuit 102. The working fluid in the working fluid circuit 102 may be introduced to the turbo pump 260 and/or the start pump 280 from the low pressure side of the working fluid circuit 102 and may exit the turbo pump 260 and/or the start pump 280 at the high pressure side of the working fluid circuit 102. The turbo pump 260 and the start pump 280 may be operative to circulate the working fluid throughout the working fluid circuit 102. In one or more embodiments, the start pump 280 may be utilized to initially pressurize and circulate the working fluid in the working fluid circuit 102. The start pump 280 may be utilized until a predetermined pressure, temperature, and/or flowrate of the working fluid is achieved within the working fluid circuit 102. When the predetermined pressure, temperature, and/or flowrate of the working fluid is achieved, the start pump 280 may be taken off line, idled, and/or turned off, and the turbo pump 260 may be utilize to circulate the working fluid during an electricity generation process.

The start pump 280 may be a motorized pump, such as an electrical motorized pump, a mechanical motorized pump, or any other suitable pump capable of circulating the working fluid in the working fluid circuit 102. In one or more embodiments, the start pump 280 may be a variable frequency motorized drive pump with a pump portion 282 and a motor-drive portion 284. The motor-drive portion 284 of the start pump 280 may contain a motor and a drive including a drive shaft and one or more gears. In some examples, the motor-drive portion 284 may include a variable frequency drive, such that the speed of the motor may be regulated by the drive. The motor drive portion may be coupled to the drive and be configured to drive the pump portion 282 of the start pump 280. The pump portion 282 may include an inlet fluidly coupled to the low pressure side of the working fluid circuit 102 and configured to receive the working fluid from the low pressure side of the working fluid circuit 102, such as from the condenser 174. In one or more embodiments, the pump portion 282 may receive working fluid from the fluid fill system 140, the mass management system 170, and/or the inventory system 180. The pump portion 282 may also include an outlet fluidly coupled to the high pressure side of the working fluid circuit 102 and configured to discharge the working fluid into the high pressure side of the working fluid circuit 102.

The turbo pump 260 may be a turbo-drive pump or a turbine-drive pump and may be configured to pressurize and/or circulate the working fluid throughout the working fluid circuit 102. The turbo pump 260 may contain a pump portion 262 and a drive turbine 264 coupled together by a drive shaft and optional gearbox. The pump portion 262 of the turbo pump 260 may be driven by a drive shaft coupled to the drive turbine 264. The pump portion 262 may include an inlet fluidly coupled to the low pressure side of the working fluid circuit 102 and configured to receive the working fluid from the low pressure side of the working fluid circuit 102, such as from the condenser 174 and/or the working fluid storage system 290. The pump portion 262 may also include an outlet fluidly coupled to the high pressure side of the working fluid circuit 102 and configured to discharge the working fluid into the high pressure side of the working fluid circuit 102.

The drive turbine 264 of the turbo pump 260 may be driven by the working fluid from one or more heat exchangers 120, 130, 250. The drive turbine 264 may include an inlet fluidly coupled to the high pressure side of the working fluid circuit and configured to receive the working fluid flowing from one or more heat exchangers 120, 130, 250 from the high pressure side of the working fluid circuit 102. The drive turbine 264 may include an outlet fluidly coupled to the low pressure side of the working fluid circuit 102 and configured to discharge the working fluid into the low pressure side of the working fluid circuit 102. In one or more embodiments, the working fluid released from the outlet of the drive turbine 264 may be returned into the working fluid circuit 102 downstream of the first recuperator 116 and upstream of the recuperator 218. In one or more embodiments, as depicted in FIG. 2, the drive turbine 264 of the turbo pump 260 may be fluidly coupled to the working fluid circuit 102 downstream of the third heat exchanger 250, and configured to receive at least a portion of the heated working fluid from the third heat exchanger 250 to drive the turbo portion 264 of the turbo pump 260.

A bypass valve 265 may be fluidly coupled between and in fluid communication with a fluid line extending from the inlet on the drive turbine 264 of the turbo pump 260 and a fluid line extending from the outlet on the drive turbine 264 of the turbo pump 260. In one or more embodiments, the turbo bypass valve 265 may be opened to bypass the turbo pump 260 while utilizing the start pump 280 during the initial stages of generating electricity with the heat engine system 200. Once a predetermined pressure, temperature, and/or flowrate of the working fluid is achieved within the working fluid circuit 102, the turbo bypass valve 265 may be closed and the heated working fluid may be flowed through the drive turbine 264 to start the turbo pump 260.

The heat engine system 200 may also include one or more control valves 261, 281 fluidly disposed within the working fluid circuit 102. The control valves 261, 281 may be flow control safety valves or check valves and may be configured to regulate the directional flow, and/or to prohibit backflow of the working fluid within the working fluid circuit 102. As shown in FIG. 2, a turbo control valve 261 is disposed downstream of the outlet of the pump portion 262 of the turbo pump 260 and a start pump control valve 281 is disposed downstream of the outlet of the pump portion 282 of the start pump 280. In one or more embodiments, the control valves 261, 281 may prevent the backflow of the working fluid in the working fluid circuit 102 and/or allow the working fluid to only flow in one direction therethrough.

One or more bypass valves 254, 256 may be independently disposed within the working fluid circuit 102 downstream of the turbo pump 260 and/or the start pump 280. The one or more bypass valves 254, 256 may be fluidly coupled to and allow fluid communication from the low pressure side and the high pressure side of the working fluid circuit 102. In one or more embodiments, the working fluid may flow from the high pressure side of the working fluid circuit 102, through the one or more bypass valves 254, 256, and to the low pressure side of the working fluid circuit 102. FIG. 2 depicts a turbo pump bypass valve 254 and a start pump bypass valve 256 independently disposed within the working fluid circuit 102 downstream of the turbo pump 260 and the start pump 280, respectively. In one or more embodiments, at least a portion of the working fluid in the high pressure side of the working fluid circuit 102 from the turbo pump 280 and/or the start pump 260 may flow through the turbo pump bypass valve 256 and/or the start pump bypass valve 254 to the low pressure of the working fluid circuit 102.

FIG. 2 depicts the throttle valve 150 disposed upstream of the second heat exchanger 130 and downstream of the start pump 280 and the turbo pump 260. The heat engine system 200 further includes a throttle trim valve 252 disposed within the high pressure side of the working fluid circuit 102, upstream of the heat exchangers 120, 130, 250, and downstream of the start pump 280 and the turbo pump 260. In one or more embodiments, the throttle trim valve 252 may be configured to control the flow of the working fluid throughout the working fluid circuit 102. In another embodiment, the throttle trim valve 252 and the throttle valve 150 may both control the flow of the working fluid throughout the working fluid circuit 102.

A control system 204 may be provided in operative connection with the heat engine system 200 to monitor and control the described operating parameters, including but not limited to temperatures, pressures (including port, line, and device internal pressures), flow meters and/or flowrates, port control, pump operation through the VFD, fluid levels, fluid density leak detection, valve status, filter status, vent status, energy efficiency conversion efficiency, energy output, instrumentation, monitoring and adjustment of operating parameters, alarms and shut-offs.

As further described, a representative control system 204 may include a suitable configured programmable logic controller (PLC) with inputs from the described devices, components, and/or sensors and outputs for control of the operating parameters. The control system 204 may be integral with and mounted directly to the heat engine system 100 or remote, or as part of a distributed control system 204 and integrated with other control systems such as for an electrical supply grid. The control system 204 may be programmable to set, control or change any of the various operating parameters depending upon the desired performance and/or process of the heat engine system 200. An operating instrumentation display may be provided as a composite dashboard screen display of the control system 204, thereby presenting textual and/or graphical data of the overall and specific status of the heat engine system 200. The control system 204 may further include a virtual display of the heat engine system 200, operational history and ranges of all parameters, with query function and/or the ability for report generation.

In one or more embodiments, the control system 204 and control logic may include the following features, functions, and operations: automated unmanned operation under a dedicated control system 204; local and remote human machine interfacing capabilities for data access, data acquisition, unit health monitoring and operation; controlled start-up, operation and shutdown in the case of a loss of electrical incoming supply power, power export connection, or any other failure event; fully automated start/stop, alarm, shut-down, process adjustment, ambient temperature adjustment, data acquisition, and synchronization; and control and power management system designed for interfacing with an external distributed plant control system 204.

The control system 204 may be communicably coupled to the throttle valve 150, the throttle trim valve 252, and/or other parts of the heat engine system 200 herein described, including but not limited to one or more bypass valves, heat exchangers, flow control valves, release valves, sensors, and/or pumps. The control system 204 may be communicably coupled through any suitable means including but not limited to wired connections, and/or wireless connections. The control system 204 may also be communicably coupled to one or more systems of the heat engine system 200 including but not limited to, the waste heat system 100, the cooling system (not shown), the fluid discharge system 170, the process system 210, the working fluid storage system 290, and/or the power generation system 127, and may be configured to monitor and/or control multiple process operation parameters within one or more systems of the heat engine system 200. In one or more embodiments, the control system 204 may be configured to actuate, adjust, manipulate, and/or otherwise control one or more parts and/or systems of the heat engine system 200. The control system 204 may also be configured to monitor one or more parameters and/or variables of the working fluid within the heat engine system 200 including, but not limited to pressure, temperature, and/or flowrate. By controlling the various part and/or systems of the heat engine system 200, the control system 204 may control the flow of the working fluid throughout the working fluid circuit 102, thereby regulating the temperature, pressures, and/or the physical state of the working fluid throughout the working fluid circuit 102.

In one or more embodiments, the control system 204 may include a computer system 206 with a multi-controller algorithm configured to monitor, actuate, adjust, manipulate, and/or otherwise control one or more parts of the heat engine system 200. The control system 204 may also be configured to implement one or more method or processes for the heat engine system 200 including, but not limited to a startup process, a normal shutdown process, a controlled blow down process, an emergency shutdown process, and/or a trip state process.

Further, in certain embodiments, the process control system 204, as well as any other controllers or processors disclosed herein, may include one or more non-transitory, tangible, machine-readable media, such as read-only memory (ROM), random access memory (RAM), solid state memory (e.g., flash memory), floppy diskettes, CD-ROMs, hard drives, universal serial bus (USB) drives, any other computer readable storage medium, or any combination thereof. The storage media may store encoded instructions, such as firmware, that may be executed by the process control system 204 or any of the other controllers disclosed herein to operate the logic or portions of the logic presented in the methods disclosed herein. For example, in certain embodiments, the heat engine systems 90 and/or 200 may include computer code disposed on a computer-readable storage medium or a process controller that includes such a computer-readable storage medium.

The heat engine systems 90, 200 described herein may provide one or more methods of managing the working fluid during one or more modes of operation. Exemplary operation of the heat engine system 90, 200 and the inventory system 180 will now be described. It should be noted that the representative operative temperatures, pressures, and flowrates as indicated or otherwise defined or described herein are by way of example only and are not in any way to be considered as limiting the scope of the disclosure.

The modes of operation may include, but are not limited to the following steps and functions. An initial fill mode, wherein the working fluid is introduced to an empty heat engine system 90, 200 to purge and fill the heat engine system 90, 200. A standby mode, wherein the working fluid is not circulated through the heat engine system 90 and warm-up systems may be active. A startup mode that may include a recirculation idle mode, a minimum idle mode, and/or a full speed idle mode. The recirculation idle mode, wherein the power turbine 128 may be bypassed by controlling the power turbine stop valve 117 and/or the power turbine bypass valve 118, the recuperator 116 may be gradually warmed, and the waste heat exchangers 120, 130 may be cooled. The minimum idle mode, wherein the power turbine 128 may be at a minimum speed (˜20k RPM) to achieve bearing lift-off. The full speed idle mode, wherein the power turbine 128 may be at a design speed (˜40k RPM) with no load and the pump 179, at least in part, maintains the speed of the power turbine 128. An operation mode, wherein the power turbine 128 may be operating at the design speed and may produce a nominal design power. In at least one embodiment, the operation mode may further include switching to a load control from a pump speed control, wherein the load maintains the turbine speed instead of the pump 179. A shutdown mode, wherein the power turbine 128 is stopped in a controlled process and the heat engine system is gradually cooled. An emergency shutdown mode, wherein the pump 179 and the power turbine 128 are stopped abruptly or quickly and the heat exchangers 120, 130 may be cooled passively.

Referring to FIG. 3, depicted is a schematic of a method 300 of managing the working fluid in a heat engine system during a system shutdown. The method 300 may include initiating the emergency shutdown mode, as at 302.

The emergency shutdown mode may be initiated by one or more failure events, including but not limited to, a full power fault, a generator load reject, a generator short circuit, and/or over-speed of the power turbine 128. In at least one embodiment, the emergency shutdown mode may include actuating the power turbine stop valve 117 and/or the throttle valve 150 to prevent the flow of working fluid therethrough, thereby reducing or stopping the circulation of the working fluid within a portion of the working fluid circuit. In one embodiment, a failure event may result in a trapped portion or volume of the working fluid in the working fluid circuit 102. More specifically, the failure event may cause working fluid to be entrained or trapped within the heat exchangers 120, 130, the fluid lines 131, 139 within the high pressure side of the working fluid circuit 102, and/or the recuperator 116. Further, during the emergency shutdown mode, the heat source stream 110 may continue to flow through the waste heat system 100 and thermal energy may continue to heat the working fluid within the heat engine system 90, thereby increasing the temperature and/or pressure of the working fluid therein. The rising temperature and/or pressure of the working fluid within the trapped volume may result in damage to the heat exchangers 120, 130 and other system components. In at least one embodiment, the pressure relief valves 113 a and 113 b may vent the working fluid in the trapped volume to relieve express pressure and prevent damage to the heat engine system 90. However, utilizing the pressure relief valves 113 a and 113 b also results in a loss of the working fluid to the atmosphere.

The method 300 may also include regulating the pressure and/or temperature of the working fluid within the heat engine system, as in 304. In at least one embodiment, the method 300 avoids a procedure that includes the venting of the working fluid through the pressure relief valves 113 a and 113 b.

A method to avoid venting the working fluid through the pressure relief valves 113 a and 113 b may include flowing the high temperature and/or pressure working fluid in the trapped volume to the low-pressure side of the working fluid circuit 102. In one embodiment, the power turbine bypass valve 118 may be actuated to allow the working fluid in the trapped volume of the working fluid circuit 102, to flow to the low pressure side of the working fluid circuit 102, thereby reducing the pressure and avoiding the venting through the pressure relief valves 113 a and 113 b. However, the temperature of the working fluid downstream of the heat exchangers 120, 130 may be greater than the temperature design limits of one or more system components in the low-pressure side. As such, the high temperature working fluid may result in damage to one or more system components in the low temperature side including the recuperators 116, the condenser 174, and/or the associated fluid lines therein. In one embodiment, the attemperation valve 162 may be actuated to allow at least a portion of the working fluid upstream of the heat exchangers 120, 130 to flow through the attemperation line 160 to a point in the working fluid circuit 102 downstream of the heat exchangers 120, 130, thereby mixing the cooler working fluid upstream the heat exchangers 120, 130 with the warmer working fluid downstream of the heat exchangers 120, 130. Thus, the attemperation valve 162 may be utilized to maintain and/or reduce the temperature of the working fluid below the temperature design limits of one or more system components.

The method 300 may also include discharging the working fluid to the inventory system 180, as in 306. In at least one embodiment, discharging the working fluid from the working fluid circuit 102 to the inventory system 180 may include cooling the working fluid, compressing the working fluid, and/or storing the working fluid in the inventory system 180. In at least one embodiment, the pressure differential between the working fluid circuit 102 facilitates the discharge of the working fluid to the inventory system 180. The discharge of the working fluid may also be accomplished through other appropriate means, including but not limited to a pump. Under nominal conditions, the pressure of the inventory tank 181 may be maintained at about 150 psi below the MAWP. In at least one embodiment, the MAWP may be determined by the inventory tank 181. For example, the inventory tank 181 may be a low-pressure tank with an MAWP of about 350 pounds per square inch (psi) (about 2.4 MPa) or less. As the heated and/or pressurized working fluid is introduced into the inventory tank 181, the pressure therein may rise and approach the MAWP, which may be about 350 psi (about 2.4 MPa). The inventory tank 181, cooled by the second refrigeration system 183, may absorb at least a portion of the thermal energy in the working fluid, thereby reducing the pressure therein. An additional portion of the working fluid maintained within the inventory tank 181 may serve as the heat sink and further absorbs at least a portion of the thermal energy therein. The first refrigeration system 182 may then be used to recover the nominal operating pressure of the inventory tank 181.

The method 300 may also include recycling of the working fluid in the inventory system, as at 308. As the heat engine system 90 is brought back online and restarted, the inventory tank 181 may serve as a source of the working fluid to recharge the system. In at least one embodiment, the inventory system 180 may be fluidly coupled to one or more systems of the heat engine system 90, and may be configured to deliver working fluid thereto. For example, the inventory system 180 may be fluidly coupled to the fluid fill system 140 and may deliver working fluid thereto for storage. The inventory system 180 may deliver the working fluid to the low pressure side of the working fluid circuit 102 upstream of the pump 179. In another embodiment, the inventory system 180 may deliver the working fluid to the mass management system 170.

The method 300 for managing the working fluid in a heat engine system may include flowing a working fluid (e.g., sc-CO₂) through a working fluid circuit 102 having a high pressure side and a low pressure side, while avoiding the waste heat system 100. The method may include actuating the attemperation valve 162 to the first position, thereby allowing the working fluid to flow through the attemperation valve 162 and through the attemperation line 160, and the fluid lines therebetween, while avoiding the fluid line 131 downstream of the throttle valve 150, the heat exchangers 120, 130, the fluid line 133, the first recuperator 116, and the power turbine 128. By avoiding the waste heat system 100 of the heat engine system 90, the working fluid may avoid the transfer of thermal energy from one or more heat exchangers 120, 130. Thus, the temperature and/or pressure of the working fluid flowing through the attemperation line 160 may be lower in temperature and/or pressure than the working fluid flowing through the waste heat system 100. Subsequently, the method may further include combining the working fluid in the attemperation line 160 with the working fluid in the working fluid circuit 102 upstream of one or more heat exchangers. The working fluid in the attemperation line 160 may reduce the temperature and/or pressure of the working fluid flowing through the one or more heat exchangers 120, 130.

The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

We claim:
 1. A heat engine system, comprising: a working fluid contained in a working fluid circuit having a high pressure side and a low pressure side, wherein a portion of the working fluid is in a supercritical state in the high pressure side of the working fluid circuit; at least one heat exchanger in the working fluid circuit, in thermal communication with a heat source stream coupled to the working fluid circuit, and configured to provide thermal energy from the heat source stream to the working fluid in the working fluid circuit; a power turbine disposed between the high pressure side and the low pressure side of the working fluid circuit, and operative to convert a pressure drop in the working fluid to mechanical energy; a recuperator in the working fluid circuit operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit; a cooler in thermal communication with a cooling medium and the low pressure side of the working fluid circuit, and operative to control a temperature of the working fluid in the low pressure side of the working fluid circuit; a turbo pump disposed in the working fluid circuit, coupled to the low pressure side and to the high pressure side of the working fluid circuit, and operative to flow the working fluid through the working fluid circuit; an attemperation line including an attemperation valve disposed therein, the attemperation line fluidly coupled to the working fluid circuit upstream of at least one or more heat exchangers and downstream of at least one heat exchanger, and configured to circumvent the working fluid around at least one or more heat exchangers; a power turbine bypass line including a power turbine bypass valve disposed therein, the power turbine bypass line fluidly coupled to the working fluid circuit upstream of the power turbine and downstream of the power turbine, and configured to circumvent the working fluid around the power turbine; and an inventory system operatively coupled to the working fluid circuit by an inventory system line, the inventory system comprising an inventory tank and at least two refrigeration systems.
 2. The heat engine system of claim 1, wherein the volume of the inventory tank is greater than the volume of the working fluid circuit.
 3. The heat engine system of claim 1, wherein the inventory tank is a low-pressure storage tank, and wherein the inventory tank has a maximum allowable working pressure rating of about 2.4 MPa or less.
 4. The heat engine system of claim 3, wherein the inventory system is configured to maintain the working fluid in the inventory tank within a temperature range from about −31° C. to about −13° C. and a pressure within a range from about 1.4 MPa to about 2.4 MPa.
 5. The heat engine system of claim 1, wherein the inventory system further comprises one or more heat sinks disposed therein.
 6. The heat engine system of claim 5, wherein the one or more heat sinks disposed therein comprise a volume of working fluid configured to absorb at least a portion of thermal energy from the working fluid discharged from the working fluid circuit.
 7. The heat engine system of claim 1, wherein a first refrigeration system of the inventory system has a greater cooling capacity than a second refrigeration system, wherein the first refrigeration system is configured to maintain the temperature of the inventory tank, and the second refrigeration system is configured to reduce thermal absorption by the inventory tank.
 8. The heat engine system of claim 1, further comprising a mass management system connected to the working fluid circuit and the inventory system, the mass management system having a working fluid vessel connected to the low pressure side of the working fluid circuit.
 9. The heat engine system of claim 1, further comprising a fluid fill system connected to the working fluid circuit and the inventory system, and configured to receive at least a portion of the working fluid from the inventory system.
 10. A method for managing a working fluid in a heat engine system during an emergency shutdown, comprising: circulating the working fluid within a working fluid circuit having a high pressure side and a low pressure side, wherein at least a portion of the working fluid is in a supercritical state; preventing the venting of the working fluid through one or more pressure relief valves by flowing the working fluid through a power turbine bypass line, thereby circumventing the working fluid around a power turbine; cooling the working fluid in the heat engine system by: flowing a first portion of the working fluid through an attemperation line, thereby avoiding the flow of the first portion of the working fluid through one or more heat exchangers; and combining the first portion of the working fluid with a second portion of the working fluid downstream of one or more heat exchangers, wherein the attemperation line is fluidly coupled to the working fluid circuit upstream of at least one heat exchanger through an attemperation valve, and fluidly coupled to the working fluid circuit downstream of at least one heat exchanger; discharging at least a third portion of the working fluid from the working fluid circuit to an inventory tank; regulating the temperature of the inventory tank during the emergency shutdown within a predetermined temperature range; and regulating the pressure of the inventory tank during the emergency shutdown within a predetermined pressure range.
 11. The method of claim 10, wherein the first portion of working fluid flowing through the attemperation line is at a lower temperature than the second portion of the working fluid downstream of one or more heat exchangers.
 12. The method of claim 10, wherein the predetermined temperature range is within a range from about −31° C. to about −13° C.
 13. The method of claim 10, wherein the predetermined pressure range is within a range from about 1.4 MPa to about 2.4 MPa.
 14. The method of claim 10, further comprising restoring the temperature of the working fluid within the inventory tank to a nominal operating condition.
 15. The method of claim 10, further comprising restoring the pressure of the working fluid within the inventory tank to a nominal operating condition.
 16. The method of claim 10, wherein the third portion of the working fluid includes a portion of the working fluid in the high pressure side of the working fluid circuit.
 17. The method of claim 16, wherein the third portion of the working fluid further includes the first portion of the working fluid flowing through the attemperation line and the second portion of working fluid downstream of the one or more heat exchangers.
 18. The method of claim 14, further comprises storing the working fluid within the inventory tank.
 19. The method of claim 18, further comprises recycling the working fluid within the inventory tank back to the heat engine system. 